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Background and Key Terms

Background

Residential wood combustion (RWC) emissions are a significant national air pollution problem and human health issue. RWC emissions occur in many neighborhoods across the country, including minority and low-income neighborhoods, and impact people in their homes. Nationally, residential wood combustion accounts for 44% of total stationary and mobile emissions of polycyclic organic matter (POM) – compounds present in the air as particles formed mainly from combustion. RWC POM accounts for nearly 25% of all area source air toxics cancer risks and 15% of noncancerous respiratory effects. RWC causes many counties in the United States to either exceed the U.S. Environmental Protection Agency’s (EPA) health-based National Ambient Air Quality Standards (NAAQS) for fine particles or places them on the cusp of exceeding those standards.

RWC from residential wood heaters contributes significantly to particulate air pollution. Exposure to particulate air pollution can result in short-term health effects ranging from irritated eyes to asthma attacks; and long-term health risks such as an increased risk of cancer, reduced lung function, and chronic bronchitis.

To address RWC emissions and health concerns, and to comply with the Clean Air Act requirements under Section 111b and Section 114, EPA revised its standards for new residential wood heaters on May 15, 2015 (Wood Heater New Source Performance Standards (NSPS)). Under the NSPS, EPA certifies wood heaters that employ the latest technology and meet the particulate matter limits established by the Wood Heater NSPS. The Wood Heater NSPS requires manufacturers to produce new wood heaters that are more efficient at burning wood and less polluting than wood heaters manufactured before 1990. Manufacturers participate in a certification program that tests a representative heater per model line rather than testing every heater. If this heater meets the EPA required emissions limit the entire model line may be certified. Historically EPA required manufacturers to certify wood heating devices using crib wood, but the 2015 NSPS allows the option to test using cord wood. See below for definitions of crib wood and cord wood. Wood heater model lines that comply with the Wood Heater NSPS are referred to as EPA-certified wood heaters.

Pursuant to the 2015 Wood Heater NSPS manufacturers may manufacture, offer for sale, or import a wood heater into the United States after applying for and obtaining an EPA Certificate of Compliance from EPA. Similarly, retailers, wholesalers, importers, and distributors of heaters may offer for sale certified heaters that have an EPA permanent label affixed to it.

Terms (NSPS Definitions)

Adjustable Burn Rate Wood Heater: a wood heater that is equipped with or installed with a damper or other mechanism to allow the operator to vary burn rate conditions, regardless of whether it is internal or external to the appliance. This definition does not distinguish between heaters that are free standing, built-in or fireplace inserts. These heaters must meet the room heater emission limits.

Catalytic Combustor: a device coated with a noble metal used in a wood heater to lower the temperature required for combustion.

Central Heater: a fuel-burning device designed to burn wood or wood pellet fuel that warms spaces other than the space where the device is located, by the distribution of air heated by the furnace through ducts or liquid heated in the device and distributed typically through pipes. Unless otherwise specified, these devices include, but are not limited to, residential forced-air furnaces (small and large) and residential hydronic heaters.

Crib wood is a specified configuration and quality of dimensional lumber and spacers, usually cut 2"x4" or 4"x4" lumber that is stapled together. This configuration was intended to improve the repeatability of wood burning emissions test methods.

Efficiency (Overall): see Overall Efficiency - HHV (%).

Emission Rate Annual Avg (lb/mmBTU) Particulate matter (PM2.5) emissions expressed in a weighted annual average of mass per unit of energy. This value is based on measurements made on the load side of the heat exchanger.

Fireplace Insert: a type of heater/stove that is designed to fit inside the firebox of an existing wood-burning fireplace (Wood Heat Organization, 2010). EPA-certified fireplace inserts are essentially wood heaters/stoves without legs or pedestals. An insert is made of steel or cast iron and is typically installed in masonry fireplaces or traditional fireplaces in order to provide effective heating (Hearth, Patio, and Barbeque Association [HPBA], 2010b).

Overall Efficiency - HHV (%): the percentage of heat that is transferred to the space to be heated when a load of fuel (e.g., firewood, pellets) is burned. Efficiency percentages listed in the table are based on an EPA-specified test method (CSA B 415-10 stack loss method). Actual efficiency will vary depending on factors such as wood moisture, appliance operation and installation (e.g., outside piping, chimney height).

Pellet Stove (sometimes called pellet heater or pellet space heater): an enclosed, pellet or chip fuel-burning device capable of and intended for residential space heating or space heating and domestic water heating. Pellet stoves include a fuel storage hopper or bin and a fuel feed system. Pellet stoves include, but are not limited to:

Residential Forced-Air Furnace: Forced-Air Furnaces (FAFs) are divided into two categories – small and large – depending on their heat output. FAFs burn wood or pellets. For each FAF category, the compliance dates and PM emission limits are as follows:

Residential Hydronic Heater: a fuel burning device designed to burn wood or wood pellet fuel for the purpose of heating building space and/or water through the distribution, typically through pipes, of a fluid heated in the device, typically water or a water and antifreeze mixture. These devices must comply with the following compliance dates and particulate matter (PM) emission limits:

Room Heater: an enclosed, wood burning-appliance capable of and intended for residential space heating or space heating and domestic water heating. These devices include, but are not limited to, adjustable burn rate wood heaters, single burn rate wood heaters and pellet stoves. Wood heaters may or may not include air ducts to deliver some portion of the heat produced to areas other than the space where the wood heater is located. Wood heaters include, but are not limited to:

Single Burn Rate Wood Heater: a wood heater that is not equipped with or installed with a burn control device to allow the operator to vary burn rate conditions. Burn rate control devices include stack dampers that control the outflow of flue gases from the heater to the chimney, whether built into the appliance, sold with it, or recommended for use with the heater by the manufacturer, retailer or installer; and air control slides, gates or any other type of mechanisms that control combustion air flow into the heater. These heaters must meet the room heater emission limits.

Step 1: Previously in compliance with the emission limits when the rule became effective on May 15, 2015.

Step 2: in compliance with emission limits 5 years after May 15, 2015.

Wood Chip Fuel: wood chipped into small pieces that are uniform in size, shape, moisture, density and energy content.

Wood Heater: an enclosed, wood burning-appliance capable of and intended for residential space heating or space heating and domestic water heating. These devices include, but are not limited to, adjustable burn rate wood heaters, single burn rate wood heaters and pellet stoves. Wood heaters may or may not include air ducts to deliver some portion of the heat produced to areas other than the space where the wood heater is located. Wood heaters include, but are not limited to:

Wood Pellet Fuel: refined and densified solid wood shaped into small pellets or briquettes that are uniform in size, shape, moisture, density and energy content.

Other Terms

Carbon Monoxide: CO is a product of wood combustion and is a colorless odorless gas. Both CO and particulate matter (PM) are a safety and health risk if breathed for too long in a confined space, but CO can be deadly in high concentrations. Manufacturers are required to test and report the CO level attained during EPA-certification testing in grams per minute.

Levels of CO, like levels of PM, that are reported for each stove do not necessarily correlate with potential levels of CO or PM in the room where the stove is located. Effective venting should not allow any leakage of CO or PM in the room. Make sure your home has a working smoke detector, especially near any bedrooms. We recommend having a smoke and/or CO detector in the same room as the wood heater for additional safety.

Cord Wood: a wood that approximates the firewood a typical homeowner would use. Cord wood testing is a better measure of how the heaters will perform on the type of fuel commonly used in homes. For home use, EPA recommends that firewood be dried to a moisture level between 15-20% to improve combustion and lower air pollutant emissions. Please see Burn Wise for more recommendations on burning more efficiently and cleaner.

Fireplace Insert: a type of heater/stove that is designed to fit inside the firebox of an existing wood-burning fireplace (Wood Heat Organization, 2010). EPA-certified fireplace inserts are essentially wood heaters/stoves without legs or pedestals. An insert is made of steel or cast iron and is typically installed in masonry fireplaces or traditional fireplaces in order to provide effective heating (Hearth, Patio, and Barbeque Association [HPBA], 2010b). These heaters must meet the room heater emission limits.

Wood Pellets: are usually made of wood from discarded wood products (sawdust, wood waste, etc.) which is compressed into small pellets. Wood pellets burn more efficiently that cord wood because of their uniform dimensions, low moisture, density and energy content.



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